Subject:
Biology
Type of Lesson:
Practical, discussion
Grade:
10
CSEC OBJ:
B 1.5 Students should be able to
explain the processes of diffusion and
osmosis using an experimental
approach
B 1.6 Students should be able to
discuss the importance of diffusion
and osmosis in living systems
Term:
Christmas
UNIT: 4
Cells
Duration:
2 x 40 mins
Lesson: 6
Diffusion and Osmosis
Week: 1
Objectives
As a result of this lesson, you will be able to:
1)
2)
3)
4)
5)
6)
explain the process of diffusion
carry out simple investigations to illustrate diffusion
explain the importance of diffusion in living organisms
explain the process of osmosis
carry out simple investigations to illustrate diffusion
explain the importance of osmosis in living organisms
Prerequisite Student Knowledge
You should be familiar with:
1) Basic knowledge of the scientific method
2) Basic knowledge of the terms ions, molecule, solute, solvent,
Important Points
Materials are made up of small particles called atoms, molecules. These particles are constantly
in motion, due to their kinetic energy. Because of this energy, the particles tend to move away
from areas where they are in plentiful supply to areas where they are scarce. This process ends
with the particles being evenly spread out throughout the particular area. Such a process of
movement is called diffusion. A special type of diffusion is known as osmosis.
Key Terms
concentration
gradient
equilibrium
selectively-permeable membrane
Challenge Areas
Look up and review definitions for the following terms:-Solute, solvent, equilibrium, gradient,
turgid, flaccid, crenated, plasmolysed, hypertonic, hypotonic & isotonic
Equipment/Material Needed:
Textbook, power-point slides, spray cologne, spray disinfectant, discs of beetroot, source of heat,
heat-proof container, water, two/three small red/green coloured sweets (gummy bears), small
amount of sugar, syrup, cane juice, water, set out in small containers, , two cups/glasses of the
same size and shape, four potato strips, cut like ‘french fries’, approximately 4 cm x ½ cm x ½
cm, two potato strips (same size as the others) which have been fried, small saucers/Petri dishes.
Note to Student
This topic offers the opportunity to learn measurement and manipulation skills. In doing the
diffusion and osmosis activities, beetroot is particularly good at showing the effects of killing
cells and negating effects of the selectively permeable membranes. Two other skills which form
an integral part of the CXC S.B.A. – ORR could also be assessed in these experiments.
Introduction
1) Introductory Activity
Introduction – 10 minutes
a. Imagine that two minibuses are available for transport, what you would do if you
were a standing passenger on both buses and the bus arrived in the Half Way Tree
terminus. At this stop most of the passengers would get off the buses. You are not
getting off here. What would you do?
You probably would move to a less packed area of the bus and try to find an available
seat.
Let us take this a little further. The numbers of people in the two buses are separated into two
groups: male & female. Bus A has 16 females, 24 males and Bus B has 12 females, 18 males.
i. Which bus is more packed?
Bus A. It has the larger number of passengers
Warning
ii. In which bus would there be a greater rush for seats?
Bus A
The sweets should be
iii. Give reasons for your answer
left for five minutes
Bus A is more packed and therefore there would be more people rushing for
before observing and
seats in this bus
describing.
Body of Lesson
1) Diffusion


a. Particles [ions and molecules] move the continuously in space. Like the people in
the packed bus when there are more passengers people bump into each other more
frequently as they try to find seats. Molecules and ions move continuously as they try
to find space. The movement of these particles is due to Kinetic Energy. This activity
is called diffusion.
b. Observe (with all senses) what is happens when you
spray cologne/ perfume in any room.
spray disinfectant spray in a room
c. Place coloured sweets provided by your teacher in a small amount of water in a
saucer/Petri dish for five minutes. Describe what happens in the saucer/Petri dish
after five minutes.
d. Look back at the first two objectives for the lesson: - at the end of the lesson you
should be able to:
i. explain the process of diffusion
ii. carry out simple investigations to illustrate diffusion
e. Let’s look again at the term diffusion. Play the video on Diffusion found at the
following link
http://www.youtube.com/watch?v=H7QsDs8ZRMI&feature=related
The term was used earlier to describe the movement of particles in space. It is defined as:
The movement of particles within a gas or a liquid from a region of high concentration to a region of lower
concentration until the concen
Notes
Try to connect to the
internet ahead of
time, so that when
you are working
through this lesson,
you can link to the
sites noted below
f. Record this definition in your notebook.
2) Practical work - Osmosis
a. Compare a sample of cane juice with one of syrup. Which is sweeter?
b. Which one of the samples has:
the most water
i. the least water
ii. the most sugar
Notes
iii. the least sugar
c. You probably observed that:
i. Syrup is sweeter than cane juice.
ii. Cane juice has more water than syrup.
iii. Syrup has less water than cane juice.
iv. Syrup has more sugar than cane juice.
v. Cane juice has less sugar than syrup.
Strips increase in size
and become hard in
water while they
decrease in size and
become soft in cane
juice.
.
d. The terms solute, solvent and solution are used to describe substances when they
are mixed with others. In these samples, - sugar is the solute, which is dissolved in
water – the solvent to produce a solution – the cane juice and syrup. The term
concentration is used to describe the amount of solute dissolved in a specific amount
of the solvent. When we use the term sweet we are actually describing the amount of
sugar which was dissolved to make the solution which we have described as sweet.
e. You are going to move on to another practical activity.
i. Place two potato strips of similar size in water and cane juice, each for five
minutes.
ii. Measure both strips and note any changes in texture of the strips.
Notes
Fresh strips were
become larger in water
not the cane juice while
fried strips will not
change in either
solution.
Boiling destroys cell
structures – membrane
organelles, resulting in
the release of the
pigments into the
solution
iii. What changes in size and texture did you observe and suggest why these
occurred.
iv.
f. Use the fried potato strips in both solutions for five minutes. Observe the sample
of potato strip that has been fried, and answer the following questions;
Which potato strips are larger after five minutes in water? The ones that were fried or
the fresh ones?
i. Why is this so?
Note. The potato strips which were fresh are larger in five minutes. The fresh ones
changed in both solutions while the fried ones did not.
g. Now place two discs of carefully washed, freshly cut, beetroot/carrot:
i. 10 ml water at room temperature
ii. 10 ml water and boil it for five minutes.
Observe carefully and noting any changes that occur.
Note. Sample “ii” becomes coloured while sample “i” does not change.
h. The two other objectives for the lesson were that at the end of the lesson you
should be able to:
i. explain the process of osmosis
ii. carry out simple investigations to illustrate osmosis
i. Think of the situation with the two buses again, and then answer the following
questions:
i. Which group is larger in each bus? [males]
ii. What should gentlemanly males do if seats close to them become available
and females are standing in the bus? [ allow the females to sit first]
j. The movement of the gentlemanly males in the bus to available seats is restricted
by the social preference which allows the females to move to available seats while the
males are permitted to sit if a female wants the seat. Like these gentlemanly males in
this situation, the movement of some particles in space, diffusion can be restricted
like the solute particles in a solution. In living organisms, the term used to describe
movement of particles when the movement of some particles is restricted while others
can move freely is called osmosis. The restricting unit is called a semi/selectivelypermeable membrane. Like the males in the packed bus, the solute molecules in
living organisms
(potato strip cells earlier), are able to be prevented from moving
into specific areas, by the cell membrane which is a selectively-permeable membrane.
However like the females the solvent molecules are allowed to pass/ diffuse through
the membrane – therefore selectively permeable to solvent molecules, from the area of
lower concentration to the area of higher concentration [causing changes in size of
the cells and texture of – potato strips] until their concentration is the same on both
sides of the membrane – an equilibrium is reached.
k. Look at http://www.youtube.com/watch?v=sdiJtDRJQEc&feature=related 2.10 –
3.10 s & http://www.youtube.com/watch?v=VUnvwrx8Wq4&feature=related
While viewing it a second time, note the following:
Notes
Try to connect to the
Internet ahead of
time, so that when
you are working
through this lesson,
you can link to the
sites noted below
During osmosis in living organisms, the solute molecules are prevented from
moving to specific areas, by the cell membrane which is a selectively-permeable
membrane.
i. However the solvent molecules are allowed to pass/ diffuse through the
cell membrane – which is selectively permeable to solvent molecules, allowing
movement from an area where there are more solvent molecules through a
semi-permeable membrane to an area where there are fewer solvent molecules
until the concentration is the same on both sides of the membrane –
equilibrium is reached.
ii. Write the definition of osmosis using the terms solute, solvent,
concentration, semi-permeable membrane and equilibrium, in your notebook.
3) The importance of diffusion and osmosis. 20 minutes
a. Suggest why the water-boiled carrot/beetroot container became coloured.
Note. Boiling actually destroyed the selectively permeable membrane removing the
restriction to the movement of coloured solute molecules from the cytoplasm of the
carrot/ beetroot cells and into the water.
b.
The final objectives for the lesson are that at the end of the lesson you should
be able to:
i. explain the importance of the process of diffusion in living organisms
ii. explain the importance of the process of osmosis in living organisms
c.
Answer the following questions:
i. Why do you use perfume/ cologne/ disinfectant spray?
[ To spread/ place gaseous molecules which they prefer to smell in / inhale from their
environment]
ii. How do they move to your nostrils? [ by diffusion]
iii. What other gas would you acquire from your environment? [oxygen]
Notes
iv. By what process do living organisms acquire gases such as oxygen and
Osmosis is the
carbon dioxide? [diffusion]
movement of solvent
molecules
v. By what process do living organisms lose gases such as carbon dioxide
from an area of lower
and water vapour? [diffusion]
concen-tration through
vi. Is diffusion important to living organisms and why? Record your answer in
a semi-permeable
membrane
your notebook.
to and area of higher
vii. Consider yourself as an example of a multi-cellular organism. Suggest how
concen-tration until
osmosis can be used to distribute water which is taken in at the mouth to all
equilibrium is reached.
cells of the body.
a. Record your response.
viii.
Is osmosis important to living organisms and why.
d.
Look at another video clip, this time of plants and osmosis found at
http://www.youtube.com/watch?v=GOxouJUtEhE Consider yourself an example of a
multi-celled organism. Suggest how osmosis can be used to distribute water which is
taken in at the mouth to all cells of the body.
4) Summary
a. Using the video clip of osmosis and diffusion by Walker found at
http://www.youtube.com/watch?v=z_u0QRsZMbk recap the following terms - solute,
solvent, solution and concentration.
b. Use these terms along with semi-permeable, equilibrium to write the definition of
diffusion and osmosis, highlighting their similarities and differences
c. While viewing this clip note the importance of both to living organisms by
outlining their roles in transport of substances into and out of cells.
Closure
Assignment
1) Write definitions of concentration, diffusion and osmosis.
2) Write notes on:
a. similarities
b. differences between osmosis and diffusion
c. the roles of diffusion and osmosis in transport of substances into and out of cells.
Out-of-Class Assignment
1) Write definitions for the following terms:-Solute, solvent, equilibrium, gradient.
2)
a.
b.
c.
d.
Suggest what changes should occur when:A limp piece of lettuce is placed in water.
Dried fruit are placed in wine for two weeks before the Christmas pudding is made.
Vendors place two week old oranges in water.
Gardeners throw salt on slugs to kill them.
3)
a. Explain the following terms:- turgid, flaccid, plasmolysis, crenation.
b. Use these terms to describe the following cells and explain what occurred when they were
placed in isotonic, hypertonic and hypotonic media/solutions.
Figure 6.1
Supplemental
Glossary of Terms
Solute
A substance that dissolves in water or another
solvent to from a solution.
Solvent
A liquid in which other substances can dissolve
concentration
The amount of solute dissolved by a solvent to
form a solution
Selectivelypermeable
membrane
Allowing some substances , but not others to
pass through
equilibrium
Both areas are of similar concentration
gradient
Describes the concentration difference between
two areas.
,
CSEC Questions
1) June 2003 Paper 3, Question 1
Note also that:
CSEC S.B.A. Skills of ORR, Measurement & manipulation skills are skills which are to be
assessed by the teacher through the procedure SBA (school-based assessment). Your experiments
may be marked by the teacher and used as part of your total ORR and M&M skill marks.
Recommended Materials
1) http://www.cellsalive.com/cells/cell_model.htm
Cell Models: An Interactive Animation
2) http://web.jjay.cuny.edu/~acarpi/NSC/13-cells.htm
The Cell
Bibliography
1) Carrington, Agard and Sealy, Biology – Skills for Excellence, London: Longman Caribbean,
1995.
2) Chinnery, Glasgow, Jones & Jones, CXC Biology, London: Cambridge University Press,
latest edition.
3) Roberts & Mitchelmore, Biology for CXC, London: Thomas Nelson, latest edition.
4) Soper & Smith with King, Caribbean Biology for CXC: An integrated approach, London:
Macmillan Caribbean, latest edition.